function lazyImg(elems){
    var arr = Array.from(elems);
    var scrollT = document.documentElement.scrollTop;
    for(var i=0;i<arr.length;i++){
        if(arr[i].offsetTop - 100 < clientH + scrollT){
            arr[i].src = arr[i].getAttribute("abc");
            arr.splice(i,0);
            i--;
        }
    }
}